Production of picric acid from monochlorbenzol

lODUCTlON OP PICRIC ACID
=KOA AONOCHLORBENZOL

STITUTE OP TECflNOLOGY

19 17

547.7

%

UNWE.^

:ij?S

PRODUCTION OF PICRIC ACID

FROM MONOCHLORBENZOL

A THESIS

PRESENTED BY

Arthur G. Fitzner and Walter Wollaston

TO THE

PRESIDENT AND FACULTY

OF

ARMOUR INSTITUTE OF TECHNOLOGY

FOR THE DEGREE OF

BACHELOR OF SCIENCE

IN

CHEMICAL ENGINEERING

MAY 31, 1917

APPROVED

ILLINO'S INSTITUTE OF TECHNOLOGY 0^<^^V^...,..^

PAUL V. galvin library ^;2^U^s.r-.Yc..t:^^^SS^^

35 WEST 33RD STREET -^ '

CHICAGO, IL 60616 .- D^ac'cf Engin«H„g S.udies

Dran of Cultural Sludi.

Picric Acid from Ohlorbenzol.

G0UT3NTS.

Page

Preface 3

Introduction 4

Theoretical Considerations ...... 6

The Process 11

Experimental Work 13

1. First Nitration. 13

2. Hydrolysis 26

3. Liberation of Dinitrophenol

from its Sodium Salt ...... 29

4. Final Nitration 32

Summary 37

Appendis: 40

Selected Bibliography 40

PHOTOS.

Ho.l^' Apparatus for Nitration and

Hydrolysis 14

No.2i,' Apparatus for Steam Distill-
ation 28

Picric Acid from ClilorTDenzol.

Preface,

This investigation into the production
of picric acid from monochlorhenzol was
undertsiken "because of the lack of literature
on the subject although the process is knoTOi
to he in extensive use. Owing to the very
limited amount of time which was available
for this work the experimenters were obliged
to confine their efforts to the application
of a certain series of reactions which appear-
ed to be most practical. As the attainment of
maximum yields at all stages was esseatial to
the success of the process considerable attent-
ion was paid to this phase of the work.

The authors desire to express their grati-
tude for the valuable assistance rendered and
interest shown throughout the work by Prof.
Harry McGormack.

Picric Acid from Ohlorbenzol,

Introduction.

Owing to the present international situa-
tion the use of picric acid as an explosive has
increased enormously. It is also used to a
very limited extent in the dye industry "but
other yellow dyes have heen found which are
less costly.

Picric Acid is the most powerful explo-
sive known and is therefore used extensively
as the bursting charge of shells. The pure
acid is exploded only hy means of a priming
charge such as a cap of mercury fulminate, hut
when traces of its metallic salts are present
it is easily exploded hy detonation. Because
of this fact great care must he taken in its
manufacture and use to prevent contamination.

The usual method for the manufacture of
picric acid is to nitrate phenol which has
heen previously sulphonated. With this process
it is impossible to obtain a sufficiently

Picric Acid from ChlorlDenzol.

pure product without recryatallization, "but
with the ehlorhenzol process the loss due to
this operation is eliminated hecause of the
high purity of the picric acid originally
obtained.

Picric Acid from Chlortenzol,

Theoretical Considerations.
^en monochlorbenzol is su'bjected to
strong nitration such as with a mixture of
concentrated or fuming nitric and sulphuric
acids at a moderately high temperature, the
resulting product is largely dinitrochlor-
henzol. It is impossihle to ohtain trinitro-
chlorhenzol by direct nitration, and "because
of this fact the production of this hody as
an intermediate could not he considered. The
first product of the nitration of chlorhenzol
consists of a mixture of ortho, meta, and
para mononitrochlorhenzols. The reaction
proceeds as follows:

C5H5CI ± HNO3 = C^H^CKUOg) * Hj,0

The three isomers have the following structural
formulae :

Picric Acid from Chlorbenzol.

NO2
ortho meta para
The amount of meta mononitrochlor"benzol
formed is less than one percent and can "be
neglected. The ortho and para derivatives are
formed in nearly equal quantities, the exact
amounts of each depending upon the temperature.
The physical properties of the ortho and para
mononitrochlorhenzols are tabulated "below:

Pr£perty_

sp .gr .
m,p»
b.p,
Crys.form.

Ortho

1.36822°

32.5°
245°
needles

Paxa_
1.52418°

24£°

monoelinic

prisms

Both forms are insoluble in water hut

Picric Acid from Chlorbenzol.

soluble in alcohol and ether. They are hyd-
rolyzed "by caustic soda solution only under
pressure at 130°.

After all of the chlorhenzol has heen
converted to the mononitrochlorhenzols the
action continues with the production of di-
nitrochlor "benzol. The reaction proceeds as
fallows :

2 no;

The main constituent of this nitration
product consists of 1:2:4 dinitrochlorhenzol,
the amount of the other possible isomers heing
limited on account of the small quantity of
meta mononitrochlorhenzol entering into the
reaction. The physical properties of the
1 :2 :4 dinitrochlorhenzol are as follows :
sp.gr., 1.697^^°: m.p., 53.5°: h.p.. 315°:
crystalline form, trimetric crystals: in-

Picric Acid from Chlorbenzol.

solulDle in water, very slightly soluble in
cold alcohol, very soluhle in hot alcohol and
ether.

At ordinary pressure and at moderate tem-
perature dinitrochlorhenzol is quantitatively
converted into sodium dinitrophenate hy the
action of caustic soda solution. The reaction
proceeds as follows :

ONa

-h^ NaOH'

NO:,

NO.

NaCI+h^O

The sodium dinitrophenate is converted
into the dinitrophenol hy acidification;

-h IS/a^SO*

The physical properties of dinitrophenol
are as follows: sp.gr., 1.683^^ : m.p., 114°:
crystalline form, yellow tablets: solubility
in water at 20°, 5 grams per 100 cc : soluble

10

Picrio Acid from CJhlorbenzol.

in aloohol and ether. Dinitrophenol may be
easily converted into trinitrophenol or picric
acid by moderately strong nitration. The reaction
is as follows :

t^a

H,0

The physical properties of picric acid
arexas follows: sp.gr., 1.767: m.p., 122.5°:
crystalline form, yellow leaf: moderately
soluble in alcohol and ether. Its solubility
in water greatly increases with an increase
in temperature as is shown in the following
table :

Temperature an_. ?icric_per_100cc_., water

OOQ. .67

20 1.10

60 2.77

80 4.22

100 6.75

11

Picric Acid from Chlor"benzol .

THE PROCESS.
Owing to the facility with which mono-
chlorhenzol is converted into 1:2:4 dinitrochlor-
henzol and the ease with Y;hich the chlorine
of the latter hody is replaced by hydroxyl "by
means of caustic soda solution, the following
process for the production of picric acid
from chlorhenzol was decided upon as being the
most practical:

The steps involved are given below:

1. The conversion of chlorbenzol to 1:2:4 di-
nitrochlorbenzol .

2. The hydrolysis of dinitrochlorbenzol to
sodium dinitrophenate .

3. The liberation of dinitrophenol from its
sodium salt.

4. The nitration of dinitrophenol to picric
acid.

In carrying out the above reactions the
experimenters attempted to determine the most

12

Picric Acid from Chlorbenzol
economical means of production.

13

Picric Acid from Chlorbenzol.

SXPBRn^HTAL WORK.

The experimental work was carried out in
four divisions corresponding to the four steps
in the process as outlined on page 11.
1. nitration.

The apparatus used in the nitration of
the chlorhenzol is shown in Photo Ho .1 on p. 14,
It consisted of a two liter flask supported
hy an iron stand and provided with a water
cooled vertical condenser. Heat was supplied
hy means of an oil hath heated hy a Bunsen
burner, and agitation was effected hy "blowing
a slow steady stream of air in at the hase of
the flask hy means of a tube inserted through
the condenser. Thermometers were used both in
the outside bath and in the nitration mixture.
At first considerable difficulty was encount-
ered in obtaining a cork or rubber stoppe*
which would withstand the attacks of the
strong hot vapors during one entire period

14

Picric Acid from Chlorbenzol,

Photo Ho.l.
^paratua for
ITitration and Hydrolysis,

15

Picric Acid from Ch.lor'benzol .

of nitration. Several innovations were tried
among them "being gold foil, lead foil, and
cement protective coatings. Of these a bar-
ium sulphate-sodium silicate cement proved
to "be the "best. A cork stopper was first
hored and fitted for the condenser, thermometer
and flask, the flask end "being made somewhat un-
size so as to allow for a heavy layer of the
cement. The condenser and thermometer were
inserted in the cork and a thick layer of the
cement forming paste was applied and allow-
ed to harden. The cork was then sealed to
the flask with fresh cement. Such a cork
withstood the disintegrating influences of
all subsequent nitrations. Temperature reg-
ulation was easily controlled by not allov/-
ing the temperature of the outer bath to
exceed that of the nitration mizture by more
than 20*^ at any time.

16

Pioric Acid from ChlorlDenzol .

Tlie nitration of. the chlorbenzol was eff-
ected by the use of several nitrating mixtures.
The possibility of a quantitative production
of dinitrochlorhenzol by means of ordinary
nitric ( sp.gr. 1.42) and sulphuric ( sp.gr.
1.84) acids was eliminated since the work of
Louis Sabinovitz and A.A.Wells : The Chemical
Engineer, Feb. -Mar., 1917, p. 24 , conclusive-
ly proved that only small amounts of dinitro-
chlorbenzol were formed under such conditions
even at elevated temperatures (200°0.).

Accordingly the first nitration was made
with a mixture of ordinary nitric ( sp.gr .1.42!
and fuming sulphuric ( sp.gr. 1.93, 20 fo free
3O3) acids. An excess of 25fo over the theore-
tical amount of nitric acid was used and suff-
icient sulphuric acid was added to bring the
water content of the final waste acid to about
20^,^. After assuming several ratios of
chlorbenzol to sulphuric acid, it was found

17

Picric Acid from Chlortenzol.

that with a proportion of 1 to 3 this water
content was approximated. A smaple calcu-
lation is given helow:

CgHp-Cl * 2 HITOJ5 = CgHjjCKlIOj,)^ * 2 H2O

112.5 126 202.5 36

Assuming 100 grams of chlorbenzol, the amount
of nitric acid ( sp.gr. 1,42,70^) theoretical-
I7 required is :

126/112.5 X IO0/.7 " 160 gms. miOg { 70^;^)
With 25fo excess - 200 gms. " "

Water in 200 gms. acid equals:

200 X .3 =60 gms. water

Water formed in the reaction equals :

36/112.5 X 100 = 32 gms. water

The amount of water absorhed by the 300 gms.,
of fuming sulphuric is :

SO3 X HgO = SgSO^

80 18 98

13

Picric Acid from Chlorlienzol.

300 X .20 X 18/80 = 13.5 gms. water a"bs.
The amount of water in the spent acid mixture is

( 60 i 32) - 13.5 = 78.5 gms. water
The total weight of spent acid is :

HgSO^(ioo::^)(30o i 13.5) :: 313.5 gms.

Water = 78.5 gms.

xs Em^{100fo){4:0x,'7) = 28.0 gms.

Total ~ 420.0 gms.
Percent of water in the acid mixture equals :

100 X 78.5/420 = 18.7 % water
In this calculation the possible loss due to
the escape of uncondensed vapors has "been
neglected.

The first nitration was therefore made with
200 gms. chlorhenzol
400 gms. KEO^i sp.gr. 1.42)
600 gms. HpSO^ ( sp.gr. 1.93)
fhe two acids were poured into the flask and
the mixture cooled. The chlorhenzol was then

19

Picric Acid from Chlorbenzol .

slowly added to the acid mixture with continual
shaking and cooling. The flask was then sealed
to the condenser. The mixture was continually
agitated "by air and heated sufficiently to
maintain a moderate reaction. The following
is a tahle of the time and temperature through-
out the operation :

Time_

Temperature

2:00 P.M.

Start

E:30

100° c.

3:00

110

3:30

140

4:00

160

4:30

160

5:00

160

5:30

160

6:00

165

Throughout the run there was a slight evolution
of hrown NOg fumes hut the amount of these was
never allowed to become great. Mien the reaction

20

Picric Acid from ChlorT)enzol.

had ceased , after about four hours, the par-
affin hath was removed and the contents of the
flask allowed to cool slightly. The oily layer
of dinitrochlorbenzol was separated from the
waste acids in a separating funnel, and was
subsequently washed several times with hot
water until free from acid. The acid mixture
was diluted with water to precipitate dissolved
dinitrochlorbenzol, and the flaky crystals
were coagulated as an oil by heating. This
portion was added to the main bullr v/hich upon
cooling to room temperature solidified. The
total yield of washed product was 345 grams.
Further work with this product showed that it
contained 10',^ of mononitrochlorbenzols . The
theoretical yield of dinitrochlorbenzol from
200 grams of chlorbenzol is :

202.5/112.5 x 200 = 355.5 gms.
The actual yield of dinitrochlorbenzol was :

345 z .9 = 310.5 gms.

21

Picric Acid from ChlorlDenzol.

The percent of the theoretical yield was there-
fore :

100 s 310.5/355.5 = 87 .4 f5

IJitration with Fuming Acids,
In order to obtain a greater yield of the
dinitrochlorhenzol a stronger nitration mix-
ture was used, the water content of the spent
acid being calculated to he about i5^. The
charge taken which corresponded to these
conditions was as follows :

200 gms . chlorbenzol
400 3BS. HHO_^( sp.gr. 1.465, 8lfo)
600 gms. HgSO^ { sp.gr. 1.93, 20^ 30^ )
The treatment was very similiar to the prev-
ious Ijiitr at ion. The log of the run was-.
Time_ Temperature^

12 :30 Start

1:00 llOOC.

1:30 125°

22

140°

150°

155°

160°

165°

165®

Picric Acid from Chlorbenzol,

Time_

2:00

2:30

3:00

3:30

4:00

4:30

The dinitrochlorlDenzol was separated from the
waste acid in a manner similiar to that used
in the previously nitration. The total yield of
mixed nitrochlorhenzols was 35E gms., of which
1^ was later found to he monochlorhenzols.
The percent of the theoretical yield was :

100 X .99 X 35Z/355.5 = 98 ^ of dinitro-

chlorhenzol .
On a similiar run with slight variations in time
and temperature of nitration suhstantially the
same results were obtained .

23

Picric Acid from Chlorbenzol .

Nitration with ^aMO^ and H2SO4.
Another method of keeping the water content
of the spent nitration acid mixture down to a
minimum is- to produce the nitrdic acid during
the reaction hy the action of sulphuric acid
( sp.gr. 1.42) on crude sodium nitrate. A few
calculations with various proportions of
chlorhenzol, sodium nitrate, and ordinary-
sulphuric acid showed that it was not practical
to reduce the water content of the waste acid
mixture helow ZOfo as too much sulphuric would
he required. Accordingly in order to influence
the reaction to a greater yield of dinitrochlor-
henzol a greater excess of nitric acid was
employed , this time 100^ excess. The amount of
sulphuric acid used was calculated to reduce the
water content of the final waste acid to ahout
20fo, To satisfy these conditions the following
proportions were used:

24

Picric Acid from Chlorbenzol.

100 gms • ehlorlDenzol
300 gms. sodium nitrate
600 gms. H2SO4 ( sp.gr. 1.84, 93fo)
The operations were very much like those
in the two previous nitrations except that at
the "beginning of the reaction more careful
temperature control was required "because of
the tendency of the action to "become violent.
The data taken from such a run was as follows

Time_

Temperature

11:30 A.M.

Start

12:00

7000.

1£:30

100°

1:00

120°

1:30

130°

2:00

140°

2:30

150°

3:00

155°

3:30

160°

4:00

165°

4:30

165°

25

Picric Acid from Chlorbenzol.

While the contents of the flask were still hot,
the oily layer of dinitrochlorhenzol was decant-
ed off into a heaker of col* water. The sodium
sulphate and acid residue was cooled by the
addifcion of sufficient cold water to dissolve
all of the sodium sulphate, all dinitrochlor-
henzol which it contained was coagulated as
an oil. This was added to the main bulk of the
oil which was then washed and allowed to
solidify as in the previous nitrations. The
yield of the crude product was 177 gms., and
since ifo was later found to be mononitrochlor-
benzols, the yield of dinitrochlorbenzols was
175.2 gms. The percent of the theoretical yield
of dinitrochlorbenzol was therefore :
100 X 175.2/355.5/2 r 98.6 5$
As the sodium nitrate meltod was obviously
the cheapest of the three methods used and the
yield was high, it seems to be most adaptable to

S6

Picric Acid from Ghlorbenzol,

the process,

2. HYDROLYSIS.
The apparatus used, in the hydrolysis of
the 1:E:4 dinitrochlorhenzol obtained by the
nitration of chlorbenzol was exactly the sazne
as that used in the nitration. A s caustic
soda solution readily reacted with the dinitro-
<h lorbenzol to form sodium dinitrophenate, no
other hydrolyzing reagents were used but
several variations of the concentration of the
alkali and of the temperature were studied.
The amount of UaOH was calculated as follows :
C6H3C1(1I02)2 * 2 NaOH = CeHgCOUa )(II02 )2 SJaCl
202.5 80 * H2O

Therefore 100 x 80/202.5 = 39.5 gms., UaOH
are required. In all of the experiments 45 gms.,
were used. The ratios of UaOH to water which
were used were 1-5,1-8,1-10,1-12, and 1-14.
Very little difficulty was encountered in ob-
taining a complete hydrolysis when the contents

27

Picric Acid from Chlortenzol .

of the flask was kept at just a boiling tem-
perature, hut in all cases there was a forma-
tion of tarry todies sufficient to discolor the
product . The formation of tarry matter by the
decomposition of the :^enate was probably due
to the more intense hydrolyzing conditions at
the start. Accordingly more cautious and slow
heating at the start of the reaction resulted
in, in the case of the dilute solutions off
caustic soda, a product that was practically
free from tarry bodies.

The solution of sodium dinitrophenate at
this stage was contaminated by small amounts
of unhydrolyzed mononitrochlorbenzols, and it
was found that these could easily be driven off
by steam distillation. A description of the
apparatus used is hardly necessary as Photo ITo.E
on page 28 shows all the essential details. A
steam bath was used under the flask containing

28

Piorie Acid from flhlorbenzol ,

Photo II0.2.
Apparatus for
Steam Distillation.

29

Picric Acid from dilortienzol .

the sodium dinitrophenate solution so as to
keep the contents near lOO^C, hut yet not high
enough to decompose the phenate into tarry
"bodies. The mononitrochlorhenzols distilling off
were weighed and checked against the nitration
operation to which they corresponded. As the
mononitrochlorhenzols have the odor of nitro-
benzene the end of the distillation was easily
detected by the ahsebce of that odor. The
warm sodium dinitrophenate solution was then
filtered in order to free it from a small
amount of insoluble impurities.
3. THB IIB3RATI01T OF
DIHITROPHENOL FROM ITS SODim SAIT.
The next main reaction, which was the
liberation of dinitrophenol from its soditm
salt solution, was accomplished by acidification,
The equation for this change has been given
elsewhere • Since ',

30

Picric Acid from Chlorbenzol.

ZQ^E^Olimzlz- 2C7H3{0H)(lI02)2-lHgS0^ S2HCL
405 368 98 72.9

The amount of sulphuric acid Mvhich is required
to literate the dinitrophenol from the sodium
salt solution fonned by the hydrolysis of 100
grams ( which was the charge used in all of
the hydrolyses ) of dinitrochlorhenzol is:
100 X 98/405 = 24.2 gms . H2SO4
24.2/1.84Z .93 = l4.3 cc .HgS04{l .84 )
Because of the excess of caustic soda used in
the hydrolysis, 20 cc, of acid were used.
■When the concentrated acid was added to the
slightly cooled phenate solution or visa versa,
a very dark brown dinitrophenol contaminated
with considerable tarry matter was obtained.
After making various changes, a light yellow
dinitrophenol precipitate was finally obtained
by slowly adding the cooled phenate solution,
with continual stirring, to an iced 10^ sulph-
uric acid solution. Even with this procedure it

31

Picric Acid from Ghlorbenzol .

was found iinpossi"ble to precipitate a light
colored dinitrophenol from a phenate solution
which had "been contaminated with tarry matter
during the hydrolysis of the dinitrochlor-
benzol, hut with careful working and the oh-
servance of the proper conditions at all steps
an excellent light yellow dinitrophenol was
always obtained. The precipitated dinitrophenol
was filtered and largely freed from water by
means of suction. The product Jims washed vTith
cold water. The partially dried phenol was
further dried on a porous plate in a steaip
closet. The theoretical yield of dinitrophenol
from 100 grams of dinitrochlorbenzol is
( see top of previous page ) :

100 X 368/405 = 90.8 gms.
The actual yield varied from as low as 66 gms.,
in the case of the dark dinitrophenol to about
95 grams in the case of the good color dinitro-
phenol. On account of the difficulty of drying
the efficiency of the process at this step

32

Picric Acid from Chlorbenzol .

could not te accurately determined. As would be
expected greater yields of dinitrophenol ■S7ere
obtained from the 99;o dinitrochlorbenzol than
from the 90fj. The process did not require the
dinitrophenol to he thoroughly dried, the dry-
ing having been made to give some idea of the
efficiency of the hydrolysis and acidification
operations.

4. PINAL NITRATION.
Ab was indicated on page 11, the last step
in the process has for its object the conversion
of the dinitrophenol obtained in the third step
to trinitrophenol or picric acid. The apparatus
used for this nitration was similiar to that
used in the nitration of the chlorbenzol. The
condenser, however, was not essential on
account of the comparatively low temperatures
{ up to llO^C. ) employed. The nitration was
carried out v/ith ordinary nitric acid( sp.gr.
1.42, 70^).

33

Picric Acid from Chlorbenzoi.

Since;

CgH3(0H)(II0g)g * HNO3 = CgH3(0H){II0g)3 * HgO
184 63 229 18

the amount of acid required for 1 gn,, of di-
nitrophenol is;

63/184 = ,342 gm. HIIO3

or .342/. 7 - .488 gm. HITO3 (SOg)
In the nitration ICO^ excess of nitric was used
and sufficient sulphuric acid ( sp.gr. 1.84)
wasoadded to make the water content of the
waste acid about ZOfj, The proportions of
dinitrophenol, nitric, and sulphuric which
gave these conditions were 1:1:2 respective-
ly. The calculations are omitted as similiar
ones have already been given. The charge was
agitated and the temperature gradually raised
in order to maintain the reaction. After about
three hours the reaction was apparently com-
pleted and the temperature had risen to about
115° G# The hot mixture was then poured into
3 or 4 times its volume of cold water.

34

Picric Acid from dilortenzol.

This gave a dense crystalline precipitate
of picric acid which was light yellow in color.
TS/hen cold the picric acid was filtered off,
washed with cold water, and dried on a porous
plate in a warm closet. With light colored
dinitrophenol very good picric acid having
a melting point in the neighborhood of 1E0°C.,
was ohtained without recrystallization, hut it
was not possible to obtain a good picric acid
from a darlr dinitrophenol by such a procedure.
Eecrystallization from water gave the acid
in the form of beautiful yellow leaves. The
theoretical yield of picric acid from 100 grains
of dinitrophenol from the equation at the top
of the previous page is :

100 X 229/184 ' 124.4 ^s.
In one run v/here the charge consisted of:
100 gms. crude dinitrophenol from 100 gms.,

of 90f5 dinitrochlorbenzol.
100 gms. HUO^C sp.gr. 1.42)

35

Piorio Acid from Chlortienzol .

200 gms. H2SO4 { sp.gr. 1.84)
a yield of 82 grams of picric acid was ob-
tained :

100 X.9 X 229/202.5 = 101.7 gms. picric

The combined efficiency of the hydrolysis,
acidification, and final nitration operations
was :

82/101.7 = 80.6 7^

The average efficiency of each of these three

operations was therefore :
3

rsO X 100 xlOO = 93.0 $

In another rim 80 grams of picric acid
was obtained from 90 grams of a total of 95
grains of crude dinitrophenol obtained from
100 gms., of 99'^ dinitrochlorbenzol. The
Theoretical yield would have been:

100 z .99 X229/202.5 x 90/95 = 106.0 ^s.
The combined efficiency of the three steps was ;
80/106 IE 75.4 fi

36

Picric Acid from ChlorlDenzol .
The average efficiency of each step was therefore

^75 .4 z 100x100 ~ = 91.0 ^J

In the two runs above the best possible
conditions were attained at all steps. The di-
nitrophenol used was practically free from
tarry matter and the picric acid obtained was
of excellent color. In other runs where darker
dinitrophenol was employed the yields were
considerably less than those ginen above.

Picric Acid from Chlorbenzol.

smaiARY.

The results obtained throughout the exper-
iments on the production of picric acid from
monochlorhenzol on a small scale were consid-
ered very favorable^ and there is every reason
to think that the results could he easily
duplicated or possibly surpassed in large scale
operations. Since the yield of dinitrochlor-
benzol from chlorbenzol in the first step of
the process was 98^ of the theoretical and as
the combined efficiency of the other three steps,
involving tne nydrolysis of the dinitrochlor-
bensol to sodium dmltropneuate, the acidifica-
tion of the latter to dinitrophenol, and the
nitration of the dinitrophenol to picric acid,
was from 75. 4^5 to 80.6^, the overall efficiency
or percent of the theoretical yield of picric
acid from chlorbenzol was: from 74^ to 79v3.
Considering the number of operations involved
in the process, this recovery can be regarded

33

Picric Acid from Clilorbenzol,

as excellent as it makes the average effic-
iency of each operation from
^ 74xLooxl00xl00

to

'^

V 792:100x!Ii00s:100 = 94.3^

In the ordinary phenol process 190 parts
of picric acid are obtained from 100 parts of
phenol, which makes the recovery about lofo
of the theoretical. In the absence of authentic
data on the costs of production of picric acid
in the phenol process and the difficulty of
estimating the costs in the chlorbenzol pro-
cess, a real rigid comparison of the two
methods is impossible. With the latest quet-
ations of phenol at 42^^ per lb,, and chlorbenzol
at 309^ per lb., and the costs of other chemicals
used in the two processes being approximately
the same, the other factors of the cost of
production could be slightly in favor of the

39

Picric Acid from GhlorlDenzol.

phenol process and still allow a sufficient
margin on the side of the chlor'oenzol process
to permit competition.

40

Picric Acid from Chlorbenzol,

APPEHDIZ.
Selected Bibliography.

DrwA. H.Sey, Snythetlc Phenol and PlcridJ Acid,
Metallurgical and Chemical Sngineering,
Vol. XIII, Oct. 1,1':^15, p. 6b6-690.

C.Ellls.L.Rabinovitz .A.A.VJells, The '^reparation
of Picric Acid and other titrated Phenols,
The Chemical Engineer, Feb. -aar. ,1917 , p. 21-5.

Kurt H.Mayer and Fredrich Bergius , Preparation
of Phenol from Chlorbenzol, Chemical Abs-
tracts. Vol. y. 1915. D.52?-62tt.